MacOS – way to reroute files downloaded from a specific domain to a new folder

This seems like a really simple issue and perhaps I'm overthinking it.

My specific use case for this is:

• I've downloaded a pdf/image/etc. from a website
• I'd like to take that file and move it from my default downloads folder to another folder (This would be a start. In the future, I'd like to do different variations of this with rules based on filetype, size, etc.).

I've looked up a number of options that don't quite get me where I want. I've read that applications like Automator, fswatch, etc. are good tools for this. I'm unsure of their specific implementation and was hoping for some insight and/or help in putting something together.

I currently use Firefox and they used to have an extension that would reroute files based on whatever given rules. This is not the case after the release of Quantum.